Structures experiencing loads or exposed to various environmental factors are susceptible to damage, such as cracking, corrosion, delamination, and the like. Damage to structures may lead to aesthetic flaws, structural degradation, inefficiencies, poor performance, and even catastrophic failure. Accordingly, the detection of damage to structures may be desirable to mitigate or prevent the occurrence of such negative consequences. In some circumstances, the negative consequences of damage to the structure can be mitigated or prevented through detection and repair of the damage.
Some structures include features that are particularly susceptible to damage or the inducement of damage. For example, cracks tend to form at and emanate from fastener holes in surfaces of certain structures, such as aircraft.